Crystallization from solution is widely used as a separation and purification technique in the pharmaceutical industry. The habit and size of crystal plays a crucial role on their properties. In this study, crystallization of needle-like crystals is investigated using both experimental and numerical approaches. The structure, nucleation and growth behaviour of Irbesartan phase A grown from 2-propanol solution are studied. Irbesartan provide a rare example of desmotropic behaviour in which tautomeric equilibrium exist in solution and individual tautomers can be isolated in the solid state. In this case, molecular modelling shows an unusually high anisotropy of the internal crystal structure, leading to the prediction of an acicular habit. Irbesartan form A is an example of crystal for which the properties are governed by internal properties rather than external properties. The influence of the growth conditions is investigated by in-situ and ex-situ monitoring namely optical microscopy and AFM. These observations show that crystals are agglomerated with the same crystallographic orientation as the individual constituent, this was explained by regular over and intergrowths as in the case of twinning. Both experimental results and molecular modelling lead to the selection of different additives. The nucleation and growth behaviour of Irbesartan phase A grown from 2-propanol solution containing additives, are studied. AFM observations at the microscopic scale give interesting information on the dependences of the surface topography on the growth conditions.
